1. Field of the Invention
The present invention relates to a mobile terminal having a push to talk (PTT) function, and more particularly to a method for updating a location of a mobile terminal having a PTT function with a low amount of signaling.
2. Description of the Background Art
Conventionally, a mobile terminal (such as a CDMA handset) that has a push to talk (PTT) function (hereinafter, referred to as a PTT terminal) allows communication with another party upon pressing a certain key, similar to a walkie-talkie function. That is, a PTT terminal transmits voice or other audio data when a user presses a PTT key, and may receive voice or other audio data while in a standby mode after releasing the PTT key.
A PTT terminal performs one-to-one or one-to-many communications, and operates in a half-duplex mode. A PTT terminal may transmit voice data in the form of packets, using a CDMA or GSM network, for example. The packets may be transmitted to their destination by using Voice over Internet Protocol (VoIP), for example.
FIG. 1 illustrates a related art process for registering a system identification (SID) when a PTT terminal moves into a new service area, or zone. A SID is an identification number, such as a five-digit number, that identifies a service area, and which is typically broadcast by base stations. Most carriers have one SID assigned to their service area.
According to the related art process illustrated in FIG. 1, when a user turns on the power of a PTT terminal, such as PTT terminals HS1 and HS2, the PTT terminal initiates a data call to a base station, such as base station BTS1, in order to register itself with a PTT server. The PTT terminal subsequently goes into an idle state. HS1, illustrated in FIG. 1, is a PTT terminal that has succeeded in registering with a PTT server, and HS2 is a PTT terminal that has failed to register with a PTT server.
When a PTT terminal moves into an area corresponding to a different SID, such as by moving from SID zone 1 to SID zone 2, or by moving from SID zone 1 into a boundary area where SID zones 1 and 2 overlap, as shown in FIG. 1, the PTT terminal sequentially initiates a zone registration call, a parameter registration call, and a data call to a base station in SID zone 2, such as BTS2, to register a SID change.
A zone registration call is a call originated from a terminal for informing a base station of its location when the terminal moves from one zone to another. A parameter registration call is a call originated from a terminal for informing a base station of a parameter change by the terminal, if a system value changes when the terminal moves from one base station to another. A data call is a call for receiving information required for a PTT service from a base station in an initial connection.
When a PTT terminal initiates a data call to a base station, the data call lasts for a duration of approximately 15 seconds. After the approximate 15 second duration, the base station sends a release message to the PTT terminal to end the data call, and the PTT terminal subsequently enters into an idle state.
Thus, as aforementioned, according to a related art process for registering a SID when a PTT terminal moves into a new service area, when the PTT moves into the new service area, the PTT terminal sends a zone registration message and a parameter change registration message to a base station to register the change of a SID, and then initiates a data call. This frequent messaging increases the load on the mobile communication system, as it requires frequent call channel allocation by a base station, thus preventing the base station from allocating call channels to other mobile terminals.
Further, during the approximate 15 second duration of the data call for registering with the PTT server, incoming calls cannot be received.